Developments in biotechnology have seen the growing use of biomolecules, such as proteins, peptides, vaccines, antibodies, antigens, nucleic acids, and growth factors as therapeutic agents. However, the creation of delivery approaches that combine high specificity for the target cell or tissue, high therapeutic payload, and modest toxicity remains a challenge. See, for example, Juliano, 2007, Biochem Soc Trans; 35(Pt 1):41-3 and Shi and Huang, 2009, Crit. Rev Ther Drug Carrier Syst; 26(1):29-84. Thus, there is a need for improved drug delivery systems for the delivery of biomolecules. Such improvements will enhance the therapeutic efficacy of such biomolecules and reduce the economic and social burdens of care for previously untreatable or only partially treatable diseases.